A major earthquake in the Sacramento-San Joaquin Delta could cause widespread levee failure and flooding, costing the state more than $30 billion in long-term losses and tens of thousands of jobs, a state official warned Tuesday.

In testimony before a joint legislative committee in Sacramento, Department of Water Resources Director Lester Snow said a 6.5 magnitude earthquake in the western Delta could tear 30 breaches in the levees that protect water supplies for 22 million Californians and some of the nation’s most productive farmland.

David Mraz, the Delta levees program manager who prepared the earthquake scenario presented by Snow, said it could take five years and billions of dollars of work to restore full water deliveries from the Delta.

In the meantime, vegetable production in the San Joaquin Valley would dry up, cities would be forced to adopt stringent water conservation measures, and some farm communities would permanently wither.

“I think there would be portions of the economy that would not fully recover,” Mraz said. “I think we would be a changed society in some senses.”

Job losses, primarily in agriculture, could exceed 30,000, and the cost to the state’s economy could total $30 billion to $40 billion, much of it in lost crop production in the first five years after the earthquake.

Mraz said farmers would turn to groundwater to sustain their more valuable crops, such as fruit and nuts,

straining groundwater supplies that are already depleted.

Snow’s testimony was the latest in a drumbeat of warnings about the perilous state of the levee system that protects the Delta, a maze of reclaimed agricultural islands and waterways that provide nearly two out of three Californians some portion of their water.

Snow said that in an earthquake, many of the earthen levees are expected to fail, flooding 3,000 homes, 16 Delta islands and letting salt water from San Francisco Bay rush toward the big pumps that send water south through the State Water Project and the federal Central Valley Project. The pumps would have to be shut down as efforts were made to repair key levees to block the salt water.

The Metropolitan Water District of Southern California, the region’s major water wholesaler, has built up a six-month emergency supply and also gets water from other sources such as the Colorado River. But other, smaller water agencies don’t have such fallbacks. And even after a year of emergency repair work, only limited water

deliveries would resume by rerouting water from the San Joaquin River to the pumps.

“We know from running out the scenario that in this type of event we will not be able to get the water supply system up and running at full capacity for a number of years,” Mraz said.

Even without an earthquake, the Delta levees are vulnerable. They were haphazardly constructed by farmers and local reclamation districts, rest on decaying peat soil and have failed for no apparent reason in good weather.

The state estimates it would take $1.3 billion to bring them to basic standards, and that does not include the kind of seismic strengthening that would help them withstand an earthquake.

The state is conducting a two-year Delta risk study, but officials are already saying that Californians will have to pick what benefits they most want from the Delta and be prepared to forego some of the other uses. Rising sea levels will compound the levee problems and the Delta’s environmental troubles are growing despite a multi-billion dollar government restoration program called CalFed.

“We have to decide — what can we save and what do we want to save — and put the resources together to try to do that,” said Les Harder, acting deputy of the water resources department.

There has been some discussion of issuing a state infrastructure bond that would include money for levee repairs. Efforts have also been made — thus far unsuccessfully — to adopt a fee program that would require water users and others who rely on the Delta to help pay for levee improvements.

And there is talk of reviving some version of an old proposal to ship water supplies around the Delta rather than through it, thereby avoiding the potential for saltwater contamination. “It may be time to consider moving a certain percentage of the water around the Delta,” Mraz said. “I don’t think you want to do 100 percnet of the (shipments) around the Delta, but maybe 50 percent is a good number, maybe 30 percent is a good number – something so that the folks south of the Delta have a secure water supply.”

Delta advocates worry that if all water shipments were diverted around the Delta, efforts to protect the Delta ecosystem would be abandoned. A proposal to build a canal around the Delta was defeated by voters in 1982 amid concerns that it would let the south take more water from Northern California. Such a system remains controversial and it would cost $5 to $10 billion and take at least four years to construct.